Snopes.com is the definitive website to find out if that too-good-to-be-true email you just got actually is too good to be true.
Now snopes has made it even easier to find out. Introducing the Urban Legends Reference Pages: 25 Hottest Urban Legends.
BTW, several years ago I “replied to all” to announce a hoax email and cited a webpage to back me up. I got an angry reply from someone on the list that I didn’t know saying “how dare I call it a hoax” and for all he knew “I created that entire website just to debunk emails like that” and implored me to “never email him again.”
I laughed and obliged. I still crack up over that.